Checking The Cylinder Head - Yamaha 25BMH Service Manual

POWR
CYLINDER HEAD

CHECKING THE CYLINDER HEAD

1. Check:
• Combustion chamber
Carbon deposits → Clean.
• Water jacket
Mineral deposits/rust → Clean.
CAUTION:
Do not scratch the contacting surface of the
cylinder head and cylinder head cover.
2. Measure:
• Cylinder head warpage
(use a straightedge and thickness
gauge)
Out of specification → Resurface/
replace.
Warpage limit
0.1 mm (0.004 in)
Resurfacing steps
(1) Place a 400 – 600 grit wet sandpaper on
the surface plate.
(2) Resurface the cylinder head by moving
it in a figure-eight motion along the
sandpaper.
NOTE:
Rotate the cylinder head several times to
ensure an even surface.
5-22
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